triangle

noun

tri·​an·​gle ˈtrī-ˌaŋ-gəl 

1

: a polygon having three sides compare spherical triangle

2

a

: a percussion instrument consisting of a rod of steel bent into the form of a triangle open at one angle and sounded by striking with a small metal rod

b

: a drafting instrument consisting of a thin flat right-angled triangle of wood or plastic with acute angles of 45 degrees or of 30 degrees and 60 degrees

3

: a situation in which one member of a couple is involved in a love affair with a third person

Illustration of triangle

• 1 equilateral
• 2 acute
• 3 obtuse
• 4 scalene
• 5 isosceles
• 6 right triangle

Examples of triangle in a Sentence

She cut the sandwiches into triangles.

Recent Examples on the Web

But none of them can say this, none of them can let their feelings be known, and, instead of a triangle, what ends up happening is three sad lines fallen in on each other, lying in a pile, waiting for someone to come along and prop them back up into a shape. —Brian Moylan, Vulture, 4 Mar. 2026

Katie Waldron Cascadia – In the world of sparring environmentalists and loggers in Coastal Oregon, a wildlife biologist, a timber worker, and a pyromaniac punk come together to form an environmental activist group and navigate a blossoming love triangle. —Katie Campione, Deadline, 2 Mar. 2026

In quiet times, families in colorful costumes throng downtown stretches, children eat copious amounts of traditional triangle cookies. —ABC News, 2 Mar. 2026

The Historical Society sent a letter to the Village Board and some village administrators, stating that after carefully reviewing the village’s Downtown Master Plan, the Historical Society has determined that the removal of the downtown triangle is contrary to that plan. —Chuck Fieldman, Chicago Tribune, 2 Mar. 2026

Word History

Etymology

Middle English, from Anglo-French, from Latin triangulum, from neuter of triangulus triangular, from tri- + angulus angle

First Known Use

14th century, in the meaning defined at sense 1

Phrases Containing triangle

• equilateral triangle
• isosceles triangle
• Pascal's triangle
• right-angled triangle
• right triangle
• spherical triangle
• triangle inequality

Rhymes for triangle

• angle
• bangle
• dangle
• jangle
• mangle
• strangle
• tangle
• wrangle
• disentangle
• entangle
• quadrangle
• untangle

Kids Definition

triangle

noun

tri·​an·​gle ˈtrī-ˌaŋ-gəl 

1

: a figure that has three sides and three angles : a polygon that has three sides

2

: a percussion instrument made of a steel rod bent into a triangle open at one corner which is played by striking with a metal rod

3

: a drafting instrument consisting of a thin flat right-angled triangle

Medical Definition

triangle

noun

tri·​an·​gle ˈtrī-ˌaŋ-gəl 

: a three-sided region or space and especially an anatomical one see anterior triangle, carotid triangle, femoral triangle, posterior triangle, suboccipital triangle